Frequency modulation (FM) is one of the most common methods of transmitting analog voice signals across a communication channel. This method has been used in a wide variety of applications including cellular communications systems in the United States, Japan, and Europe.
A conventional analog approach to demodulating FM signals employs a discriminator followed by baseband audio processing. Although analog FM demodulators are adaptable to portable applications such as cellular communications, this approach has several drawbacks due to the tuning requirements of the analog discriminator and the direct current (DC) offsets inherent in analog circuitry.
A digital approach to FM demodulation, on the other hand, avoids the aforementioned problems of analog discriminator circuitry. A conventional digital FM demodulator requires a high-speed analog-to-digital (A/D) conversion of intermediate frequency (IF) or baseband in-phase and quadrature (I/Q) signals. After conversion to the digital domain, digital signal processing (DSP) circuitry extracts the modulating signal from the digital information. Unfortunately, size and current drain requirements typically render conventional digital FM demodulators impractical for low-cost, portable applications.
Thus, there is a need for an FM demodulator that not only avoids the problems common to analog discriminator circuitry, but also offers a reduced size and power consumption alternative to conventional digital FM demodulators.